Recently，researchers investigated the foraging profiles of bird species in two separate eucalypt forests in Australia Dryandra in Western Australia and the Southern Tablelands，roughly 3000 km east in New South Wales. Despite their geographical separation，there is a broad overlap in species between the two locations. However，at Dryandra，a much larger proportion of species (61 percent) than at the Southern Tablelands (34 percent) are ground foragers.
The high proportion of ground forages in Dryandra might be explained by the openness of habitats there，that is，the absence of dense ground vegetation，and the lack of a continuous shrub layer. Ground foraging appears to be facilitated by an open habitat with areas of bare ground. However，the researchers found that the Tablelands were also open with sparse to dense litter layers，abundant in woody debris，and had discontinuous or absent ground and shrub layers. Thus，differences in habitat structures between these areas and Dryandra cannot entirely explain the greater abundance of ground foragers in Dryandra.
The researchers offered several hypotheses to explain the difference. First，there may be important differences in habitat structure that are not revealed by casual observation. For example，differences in tree heights and canopy complexity may contribute to differences in species richness and foraging behavior among bark- and foliage-foraging birds. Second，despite structural similarities，it is possible that there are differences between habitats in the abundance or availability of litter and ground dwelling prey. Such differences，if they exist，may indicate fundamental differences between eucalypt ecosystems in how and where energy and nutrients are cycled，as well as in overall productivity. Finally，the differences in foraging profiles between Dryandra and the Tablelands may be the result of historical changes in bird species as a consequence of changed grazing and fire regimens，the impact of introduced predators， such as foxes and feral cats，and logging following European settlement. The greatest impact of these processes is on ground-foraging and ground-nesting birds. Dryandra had not been free of these changes，but the impact may have been less or more recent with the result that Dryandra may retain a more natural or complete bird diversity relative to the Tablelands.
1. Which of the following best describe the organization of the second paragraph?
(A) A thesis is proposed and supporting examples are provided.
(B) A thesis is presented，considered，and then rejected.
(C) opposing views are described and the evidence on which they are based is evaluated.
(D) An argument is described，rejected，and then an alternative is proposed.
(E) A hypothesis is presented，weighed，qualified，and then reaffirmed.
2. Which of the following best describes the function of the highlighted sentences in the context of the passage as a whole?
(A) It reconciles two conflicting theories discussed earlier in the passage.
(B) It provides an example of a general tendency described earlier in the passage.
(C) It suggests the relevance of phenomena mentioned in the previous sentence.
(D) It provides support for a claim made in the first paragraph.
(E) It provides evidence for a hypothesis discussed in the second paragraph
3. The passage suggests which of the following about “canopy complexity”?
(A) Decreased canopy complexity can lead to a greater abundance of ground foragers.
(B) Increased canopy complexity usually helps in retaining a more natural bird diversity.
(C) Increased canopy complexity is usually detrimental to ground-nesting species.
(D) Differences in canopy complexity between two regions are not always obvious.
(E) Differences in foraging behavior among foliage-foraging birds can lead to differences in canopy complexity.
4. The author suggests which of the following about “foxes and feral cats”?
(A) They may have benefited from the logging that followed European settlement.
(B) They probably affect the overall productivity of the ecosystem.
(C) They feed primarily on ground-foraging birds.
(D) They rarely， if ever， feed on tree-nesting birds.
(E) They may have had a smaller impact on Dryandra than on the Tablelands.
参考答案：B C D E
The finding that there were rock-melting temperatures on asteroids for sustained periods is puzzling：asteroids' heat source is unknown，and unlike planet-sized bodies，such small bodies quickly dissipate heat. Rubin suggests that asteroids' heat could have derived from collisions between asteroids. Skeptics have argued that a single impact would raise an asteroid's overall temperature very little and that asteroids would cool too quickly between impacts to accumulate much heat. However，these objections assumed that asteroids are dense，solid bodies. A recent discovery that asteroids are highly porous makes Rubin's hypothesis more plausible. When solid bodies collide，much debris is ejected，dissipating energy. Impacts on porous bodies generate less debris，so more energy goes into producing heat. Heat could be retained as debris fall back into impact craters，creating an insulating blanket.
1. The passage suggests that one factor that has made it difficult to account for the temperatures once reached by asteroids is
A. a miscalculation of the frequency of asteroid collisions
B. a misconception about asteroids' density
C. a mistaken assumption about what the heat source of the asteroids was
D. an underestimation of the rate at which small bodies lose heat
E. an erroneous view of how asteroids were formed
Consider each of the choices separately and select all that apply.
2. It can be inferred from the passage that Rubin disagrees with skeptics mentioned in the passage about which of the following?
A. Whether porous bodies generate less debris when struck than do solid bodies
B. The temperatures asteroids would have to reach for their rocks to have melted
C. The likely effect of impacts on asteroids'temperatures